A 68-year-old patient with recurrent perianal erythematous plaques and oozing with itchiness for 3 years sought treatment for eczema. Recently, we used “skin biopsy” to identify the cause of the disease and free him from the disease. Through the dermatopathological examination, the diagnosis of “eczema-like carcinoma outside the breast” was made clear, which gave him a clear answer to the difficult disease that had been troubling him for many years, thus indicating the correct direction of treatment. Dermatopathology is a new discipline developed from dermatological science, which is decisive for the diagnosis of certain skin diseases. The use of dermatopathology diagnostic technology can clear the fog and relieve the pain for more patients with skin difficulties. This is why there is a saying in the industry that skin biopsy is the golden key to unraveling difficult skin diseases. Skin pathology is an important diagnostic technique that uses a skin biopsy drill or minor surgery to remove a small portion of the skin of a lesion and observe its changes under the microscope after fixation and staining. Its important role in the diagnosis of skin diseases, especially tumors and degenerative diseases and other difficult diseases, cannot be replaced by other laboratory tests. The skin is an important organ of the human body. The pathological changes of the skin are similar to those of other organs, including inflammation, congestion, anemia, atrophy, hypertrophy, necrosis, and degeneration, as well as hyperplasia and tumor development. However, the structure of the skin has its own characteristics, so it also has its own special pathological changes. Currently, dermatopathology has become an important sub-discipline of dermatology, and the content is constantly enriched, and the application of histochemistry, ultrastructural examination, immunoelectron microscopy, etc. has further improved the level of dermatopathology. There are more than 1400 types of dermatological diseases, and their clinical rash manifestations are variable and some lack specificity, so that diagnosis can be made only with the help of various laboratory tests and biopsies. Second, the skin is an integral part of the human body, and many skin diseases are manifestations of systemic diseases or their components. Skin pathological examination can not only assist in clinical diagnosis and patient treatment, but also help in the occurrence, development and regression of diseases, as well as understanding the systemic state of the body. In addition, because the skin tissue is located on the surface of the body, not only the clinical manifestations can be closely integrated with the pathology, but also in the different course of the disease, according to the need to continue to observe the histopathological changes; at the same time in the skin for biopsy is also relatively simple and less risky. Histopathology of the skin has favorable conditions not found in any other organ of the body, so the importance and objective need for histopathology of the skin is increasing and has become an indispensable part of the daily diagnostic and research work of dermatologists.